1. Technical Field
The present invention relates to a data line driver that drives data lines of a display panel such as a liquid crystal display (LCD) panel. Furthermore, the invention relates to a semiconductor integrated circuit device incorporating such a data line driver, an electronic appliance that uses a display panel driving circuit including such a data line driver, and the like.
2. Related Art
For example, an LCD panel that uses high-temperature poly-silicon (HTPS) thin film transistors (TFTs) are required to have multi-gradation (high definition) and drive data lines at an ultra-high speed. Particularly when one line's worth of pixels in the LCD panel are sequentially driven by a limited number of gradation voltage generating circuits included in a data line driver, it is necessary to cause gradation voltage output from a gradation voltage generating circuit to rise and fall in a short time in response to a change in image data.
To this end, conventionally, an operational amplifier for use in a gradation voltage generating circuit is configured to increase stationary current flowing the differential stage or increase the ability of the output transistor so as to increase the ability of the operational amplifier. However, increasing the stationary current in the differential stage and the output stage leads to an increase in power consumption.
Another method is also conceivable in which a highly accurate amplifier that determines the final gradation voltage and a high drive amplifier that quickly changes gradation voltage upon a change in the level of gradation are connected in parallel so as to drive the data lines at a high speed. This method, however, is problematic in that the high drive amplifier has a high level of driving ability and thus often oscillates due to load.
JP-A-2011-172203, which is an example of related art, discloses an operational amplifier capable of achieving a high slew rate without increasing stationary driving current, and a liquid crystal driving apparatus that uses the operational amplifier. The operational amplifier includes at least one differential input unit that generates a voltage signal corresponding to the potential difference between a non-inverting input signal and an inverting input signal by using a differential pair composed of a pair of transistors, an output unit that generates an output signal having a logic level corresponding to the voltage signal generated by the differential input unit and outputs the output signal, at least one auxiliary current generating unit that detects a rapid change in the non-inverting input signal or the inverting input signal and generates auxiliary current, and a driving current generating unit that generates driving current for driving the differential input unit by summing a predetermined reference current and the auxiliary current.
However, with the operational amplifier disclosed in JP-A-2011-172203, the driving current for driving the differential input unit is increased to achieve a high slew rate after detection of the rapid change in the non-inverting input signal or the inverting input signal, which causes a time difference between the occurrence of the change in the input signal and achieving the high slew rate, and results in a slow response.
JP-A-2011-172203 is an example of related art (paragraphs [0011] to [0013], FIG. 1).